My brother-in-law just got central air installed on his heat system. They replaced the furnace too. They did nothing to the duct system. The contract said they would do nothing to the duct system. Many parts are unwrapped.

My question is:
Being proffessionals, shouldn't we be held liable if we do work that causes damage to another part of the system or house. Every proffessional knows unwrapped supply pipes will quickly rust away on an AC system. Low balling a job by not including a critical part seems unethical as well as illegal to me.
Once I went white water rafting with a lawyer friend. He told me the liability waiver, we had to sign, was illegal. He said you can not sign away risks that you do not know about. Same would apply to the above contract.

This guy also put 1 ton worth of duct work on a new 2.5 ton system installed upstairs and overcharged both systems. Every register upstairs is sweating bad. This job has a place in the wall of shame.
I told my brother-in-law, he could sue the guy to complete the upstairs system and might be able to sue him to wrap the downstairs system.